Method:Place saucepan on your stovetop and melt the butter on a medium heat.Once your butter has almost melted add your sugar and stir until it has dissolved into the butter then remove from the heat and set aside to cool for about 10-15 minutes.Add the egg and vanilla essence and mix well.Add the cocoa and mix to ensure all the ingredients combine.Stir through the crushed biscuits ensuring that they are coated in the chocolate fudge mix.Press into your prepared slice tin and refrigerate until set (approx 3-4 hours).Top with chocolate icing. To make the chocolate icing place butter in a medium sized bowl with the icing sugar and cocoa, add hot water and stir with a large spoon to combine.To serve cut into squares and enjoy. Any left overs should be stored in an airtight container in the refrigerator.